That's because players usually evaluate "balance" in context of what is a "good deck" or a "bad deck". That's fine - they are not supposed to think in design terms and health of the overall game. But thinking that a deck/card is broken because of a format it is in creates a few paradoxes - first, you can have a card that's absolutely bonkers broken in one format (ADP) and then it's just kind of okay after a few sets releases (also ADP). This makes it impossible to define what a "broken" card is beyond "it has a lot of meta% and I don't like it" and makes it so a card, despite having the exact same text printed on it, can shift from broken to unbroken depending on context. Second, you can have a deck that's made out of absolutely completely fair cards, in a fair format, and be an absolutely dominant Tier 0 force (very rarely happens, but it can) just because it flows extremely well. To define this as "broken" makes it, again, completely subjective.
Even the example you've provided showcases how subjective that is - Haymaker was considered an unbeatable powerhouse but, going back to Base Set with the knowledge we have now, players have constructed stall decks that just demolish Haymaker on the spot. So, where is the "broken"? Did it change with time, despite the format being literally the same for decades?
In design terms, "broken" game elements close up design spaces, invalidate mechanics, make players misinterpret mechanics, etc. The main culprit of Base Set was not Hitmonchan, it was Energy Removal - a card that allows you to invalidate a core mechanic for the price of one card. ADP was always stupidly broken as a combination of the awful triple-prizer mechanic and an attack that invalidated the existence of single-prize Pokemon. Rain Dance, at least from the formats I know it from, always had the misfortune of being overshadowed by something really dumb - whether it's Magnezone in SM, Base Set Blastoise in a Base Set format, or Baxcalibur in the hell of a format we have now. But that doesn't change the evaluation - the game is better when it doesn't exist.